Wear and fracture mechanisms of sputtered low-friction TiAlSiN:MoS2 thin films

Coating cutting tools with TiAlSiN thin films increases their lifespan; however, this still requires wet lubrication. Here, we demonstrate the viability of low-friction TiAlSiN thin films coupled with dry lubrication through molybdenum disulfide (MoS2) alloying (TiAlSiN:MoS2) under varying alloying levels and exaggerated uniaxial loading to understand the fracture mechanisms. The films were fabricated through reactive magnetron sputtering, achieving 45% reduction in the coefficient of friction (CoF) upon introducing MoS2, compared to a reference film. The film with the lowest MoS2 (3.6 at.%) exhibited the lowest CoF (∼ 0.0525) – owing to the formation of a MoO3/MoxOy tribofilm, the highest S/Mo ratio (1.8), c-TiAlN crystal phases (in Si3N4 matrix), and ordered 2H-MoS2. It also showed moderate hardness (∼5.6 GPa), elastic modulus (∼130 GPa), H/E (∼0.04), and H3/E2 (∼0.01 GPa) ratios, excellent resistance to fracture, and minimal oxidative degradation. This film displayed a good balance between the desired structural and tribological properties for self-lubricating thin films. Lastly, an increase in MoS2 transformed the fracture and wear mechanisms of the films: ductile – abrasive degradation to brittle – oxidative degradation, associated with the oxidation of MoS2. This study establishes a practical framework for the design, fabrication, and performance evaluation of self-lubricating TiAlSiN:MoS2 coatings for advanced cutting tool applications.